The present invention is generally directed to a sonic drill head. Sonic drill heads generally impart a vibratory force and send high frequency resonant vibrations down a drill string to a drill bit. The sonic drill head combines this vibratory force with a slow rotation of the drill string to ensure that the energy applied and wear resulting from drilling are evenly distributed at the drill face. Vibration generators for sonic drilling may be housed with a rotary drive or may be a stand alone component of a drill string. The frequency of vibration is generally between 50 and 120 hertz (cycles per second) and the drill operator controls the frequency of the vibrations to match the natural frequency of the drill string to take advantage of the resonance effects of the drill string and/or to suit the specific conditions of the soil/rock geology. The resonance created at the selected frequency magnifies the amplitude of the drill bit thereby allowing for fast and easy penetration through many geological formations.
Since sonic drilling obtains its results through the combination of resonant vibrations superimposed upon a slow drill rotation, sonic drill heads are generally designed and constructed with no consideration of operating the drill with a high-speed spindle rotation suitable for traditional diamond core drilling or other rotary drilling methods. Sonic drill heads known in the art do not efficiently provide the ability to rotate the spindle at high speeds without vibration such that the drill head can additionally perform traditional diamond core or other rotary drilling methods. Further, either the vibration generator or the rotation drive of existing sonic drill heads is often located directly above the spindle within the drill head that receives the drill string. In one existing drill head, the vibration generator or rotation drive is directly above the spindle thereby preventing the passage of water, drilling fluids, mud, cuttings and/or tooling, or any other materials through the top spindle to or from the drill string and drill head. Other existing drill heads have been adapted to provide a narrow passageway to facilitate the injection of water or drilling fluid to aid in drilling. The passage of materials through the spindle to or from the drill string is generally not a consideration in sonic drill heads currently in use because the slow rotation of sonic drilling does not generally generate the same drilling conditions of other higher speed rotary drilling methods that often require passage of materials through the drill string to aid in the drilling process. As a result, existing sonic drill heads do not currently allow the passage of cuttings through the top of the drill head that are desirable when performing deep drilling. Further, existing sonic drill heads do not currently allow the passage of downhole instrumentation, and/or tooling through the top of the drill head which may be desirable when monitoring downhole conditions while drilling.
Therefore, a need exists in the art for a sonic drill head that allows an operator to perform both sonic drilling—slow rotary motion superimposed to the vibratory motion—and high speed rotary drilling. Accordingly, an additional need exists for a sonic drill head that allows the passage of drilling fluids, mud, cuttings or tooling to be introduced or removed as necessary through the top of the drill head.